From: Dumitru Ceara <dceara@redhat.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: gcc-help@gcc.gnu.org
Subject: Re: Potentially false-positive -Wstringop-overflow= warning with gcc >= 11.1
Date: Fri, 28 Jan 2022 17:16:58 +0100 [thread overview]
Message-ID: <ae2014d7-1642-0ca2-b621-e080aa76e66d@redhat.com> (raw)
In-Reply-To: <20220128152748.GD614@gate.crashing.org>
On 1/28/22 16:27, Segher Boessenkool wrote:
> On Fri, Jan 28, 2022 at 04:01:36PM +0100, Dumitru Ceara via Gcc-help wrote:
>> void *l4data = p.l4_ofs != UINT16_MAX ? (char *) p.base_ + p.l4_ofs : NULL;
>> struct hdr2 *h2 = l4data;
>>
>> memcpy(h2 + 1, &somedata[0], 6);
>
> l4data can be 0, and everything false apart from there on.
>
In general, yes, l4data can be 0, if p.l4_ofs == UINT16_MAX, which can
only happen if pkt_bar() changed p.base_.
But the compiler can't know that for sure and the warning makes it sound
like it's a sure thing:
"warning: ‘memcpy’ writing 6 bytes into a region of size 0 overflows the
destination"
In particular [0], we know for sure that l4data will not be NULL and we
can avoid the warning with an extra assertion. It's just a bit
inconvenient I guess.
In any case, thanks for the quick response!
Regards,
Dumitru
[0]
https://github.com/dceara/ovn/commit/4796a6c480d5d2e35ec2e20ed0ae23ab787fa175
next prev parent reply other threads:[~2022-01-28 16:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-28 15:01 Dumitru Ceara
2022-01-28 15:27 ` Segher Boessenkool
2022-01-28 16:16 ` Dumitru Ceara [this message]
2022-01-28 17:37 ` Segher Boessenkool
2022-01-31 21:49 ` Martin Sebor
2022-01-31 22:01 ` Segher Boessenkool
2022-02-01 8:21 ` Jonathan Wakely
2022-02-01 5:18 ` Richard Sandiford
2022-02-01 14:42 ` Segher Boessenkool
2022-02-01 23:54 ` Martin Sebor
2022-02-02 10:12 ` Jonathan Wakely
2022-02-02 18:33 ` Segher Boessenkool
2022-02-02 20:44 ` Jonathan Wakely
2022-02-02 18:23 ` Segher Boessenkool
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